Rhenium is rare metal slightly entrained in molybdenite, which is molybdenum raw ore, or copper ore. It is important metal used as an element to be added to a catalyst, an element to be added to a thermocouple or a super heat resisting alloy, a high-vacuum electron tube material or the like.
As one of promising raw materials for industrially collecting rhenium, crude rhenium sulfide is exemplified. Zinc, bismuth or the like are typical impurities in the crude rhenium sulfide.
Hitherto, as described in JP-A-S62-148327 (Patent Literature 1), a method for producing potassium perrhenate from crude rhenium sulfide has been known. In the Literature, the crude rhenium sulfide is oxidized and leached using an oxidizing agent such as hydrogen peroxide, and hydrogen sulfide is added to post-leaching solution, thereby obtaining perrhenic acid with high purity in the solution. Then, the potassium perrhenate is produced by adding potassium hydroxide thereto. As described in JP-A-H2-20575 (Patent Literature 2), ammonium perrhenate can be produced from potassium perrhenate by a method of bringing the potassium perrhenate into contact with a cation exchange resin and then neutralizing the resultant material with aqueous ammonia and performing filtration, or the like. The ammonium perrhenate is marketable as a valuable material, and in a high value-added form.
Also, JP-A-S47-21323 (Patent Literature 3) describes a method for producing rhenium, characterized by roasting rhenium-containing molybdenum raw ore, extracting the resulting material with water, adding potassium chloride to this extract, dissolving a thus obtained precipitate into concentrated sulfuric acid, adjusting sulfuric acid concentration to 1 to 3 mol/l and then conducting extraction using an organic solvent containing a high-molecular-weight organic tertiary amine in a concentration of 0.02 mol/l or more, subsequently applying back extraction to this extract with an aqueous solution of caustic potash, and applying concentrated reduction treatment to this extract.
Further, Patent Literature 3 discloses that rhenium is contained in a form of rhenium sulfide, the rhenium sulfide is oxidized and converted into rhenium oxide (Re2O7) by roasting, the rhenium oxide is vaporized at a temperature of 150° C. or higher, and accumulated in flue dust. The Literature also discloses that, if the flue dust is subjected to extraction with water, the rhenium oxide (Re2O7) is absorbed into an aqueous solution, and that the aqueous solution contains a large amount of sulfur dioxide or sulfur trioxide, and therefore shows strong acidity.